The invention relates to the field of making material, in particular granular or particulate material, collide, with the object of breaking the grains or particles.
According to a known technique, material can be broken by subjecting it to an impulse loading. An impulse loading of this kind is created by allowing the material to collide with an impact member, for example a wall, at high speed. It is also possible, in accordance with another option, to allow particles of the material to collide with each other. The impulse loading results in microcracks, which are formed at the location of irregularities in the material. These microcracks continuously spread further under the influence of the impulse loading until, when the impulse loading is sufficiently great or is repeated sufficiently often and quickly, ultimately the material breaks completely and disintegrates into smaller parts. To break the material, it is a precondition that the impact member be composed of harder material than the impacting material; or is at least as hard as the impacting material. The degree of comminution achieved, or breakage probability, increases with the impulse loading. Impact loading always results in deformation and, often considerable, wear of the impact member.
The movement of the material is frequently generated under the influence of centrifugal forces. In this process, the material is centrifugally thrown from a quickly rotating vertical shaft rotor, in order then to collide at high speed with an impact member which is positioned around the rotor. The impact member (impact face) can be formed by a hard metal face (armoured ring), but also by grains or a bed of its own material (autogenous ring). The later case is an autogenous process, and the wear during the impact remains limited. It is also possible to make the particles collide with an impact member that co-rotates with the rotor at a greater radial distance than the location from where the particles are centrifugally thrown.
The impulse forces generated in the process are directly related to the velocity at which the material leaves the rotor and strikes against the stationary or co-rotating impact member. In other words, the more quickly the rotor rotates in a specific configuration, the better the breaking result will be. Furthermore, the angle at which the material strikes the impact member has an effect on the breaking probability. The same applies to the number of impacts which the material undergoes or has to deal with and how quickly in succession these impacts take place.
A distinction can be drawn between single impact crushers, in which the material is loaded by a single impact, indirect double impact crushers, in which the material is accelerated again after the first impact and loaded by a second impact, which process can be repeated further, and direct double impact crushers, in which the material is loaded in immediate succession by two or more impacts which can be achieved by throwing the material against the co-rotating impact member: Direct double impact is normally preferred, since this considerably increases breakage probability, because during co-rotating impact the particles are simultaneously loaded and accelerated for direct successive secondary impact, with secondary impact velocity exceeding primary impact velocity; while energy consumption is virtually similar to single impact (indirect double impact doubles energy consumption).
In the known single impact crushers, the impact faces, which form an armoured ring around the rotor, are generally disposed in such a manner that the impact (stone-on-steel) in the horizontal plane as far as possible takes place perpendicularly. The specific arrangement of the impact faces which is required for this purpose means that the armoured ring as a whole has a type of knurled shape with numerous projecting corners. A device of this kind is known from U.S. Pat. No. 5,248,101. In the known method impact is heavily disturbed by the projecting corners which affects up to two-thirds of the particles. This causes wear rate along the armoured ring to be extremely high, while breaking probability is reduced significantly. Unfortunately, remaining elastic energy (rebound velocity) cannot be used to produce direct double impact because it is virtually impossible to locate secondary impact plates in an effective position. Only single impact can therefore be achieved. The centrifugal acceleration phase which does not contribute to the loading of the particle, but causes heavy wear along the impeller blade which is a major cause of concern with these type of crushers.
Instead of a stationary armoured ring a stationary trough structure may be disposed around the edge of the rotor, in which trough an autogenous bed, or autogenous ring, of the same material builds up. The centrifugally thrown material then strikes (stone-on-stone) the autogenous ring. A device of this kind is known from EP 0 074 771. The level of comminution of the known method is however limited, and the crusher is primarily employed for the after-treatment of granular material by means of rubbing the grains together, and in particular for xe2x80x9ccubingxe2x80x9d irregularly shaped grains. U.S. Pat. No. 4,575,014 has disclosed a device with an autogenous rotor blade, from which the material is centrifugally thrown against an armoured ring (stone-on-steel) or a bed of the same material (stone-on-stone).
U.S. Pat. No. 5,863,006 discloses a method for simultaneously loading and accelerating material that is metered on a horizontally disposed meter face which rotates about a vertical axis of rotation; this meter face is however separately supported on bearings and is as a whole carried by a vertical shaft which also carries a cylindrical rotor which wall is positioned concentrically around the meter face. Because of the separate bearing the meter face rotates at a lower velocity than the rotor. The material is supposed to be centrifugally thrown from this meter face and to collide with the wall of the rotor, which rotates at a much higher peripheral velocity than the meter face; and to build up an autogenous wall of own material, that acts as a co-rotating autogenous ring. This way co-rotating autogenous impact is supposed to take place with a high (relative) velocity, while wear is limited to a minimum. The material is then led to leave the rotor via ports in the wall and is then thrown against a stationary autogenous ring which is situated around the rotor for secondary autogenous impact. The comminution intensity during primary impact is however limited because the material is actually xe2x80x9cfloating freelyxe2x80x9d from the meter face (the material does not feel this rotating face) towards the co-rotating autogenous impact face, along which trajectory the particles are gradually accelerated and taken up in the autogenous ring. The intended level of impact does not materialize. Moreover, it is very difficult to keep a rotor, containing such xe2x80x9chugexe2x80x9d autogenous ring, in balance; this requires special measures to be taken, which are described in U.S. Pat. No. 5,863,006 and makes the construction extremely complicated. The known method does not essentially differ from the method disclosed in DE 31 16 159.
A much better level of comminution intensity and comminution efficiency is obtained with a known method for direct successive double impact generated by a co-rotating impact member, which is disclosed U.S. Pat. No. 5,860,605 and is in the name of applicant. This known method, the synchrocrusher, features the synchroprinciple which allows for simple design, utilization of the principle of relativity, universal synchronization and above all provides fully deterministic behaviour. The material is metered on a meter face, central on the rotor, and from there taken up by guide members which are positioned around the meter face and are relatively short and preferably aligned backwards. From these guide members the material is centrifugally thrown, with a relative low take off velocity, into the direction of co-rotating impact members which are located at a greater radial distance from the axis of rotation than the guide members. During co-rotating impact, which proceeds in a fully deterministic way, the particles are simultaneously loaded and accelerated. After co-rotating impact the accelerating particles, or particle fragments, are being thrown against a stationary impact member which is disposed around the rotor. The power generated by this combination is unsurpassed in comminution technology. The known synchrocrusher delivers full impact loading, which makes it possible to achieve a level of commninution intensity and efficiency that exceeds all commercial available comminution methods. Each particle is uniformly and accurately loaded by unimpeded double impact. Both primary and secondary impact are achieved at specified impact velocities, at selected angles of impact and at fixed impact locations. Primary impact takes place against a co-rotating impact member. Secondary stationary impact, which is generated solely by residual energy, exceeds primary impact velocity and takes place against either an armoured ring (direct double stone-on-steel impact) or an autogenous ring (a combination of stone-on-steel and stone-on-stone impact). Because primary impact proceeds undisturbed and secondary impact is obtained free of charge, outstanding performance is obtained: The known synchrocrusher makes it therefore possible to double the impact intensity achieved by a conventional stone-on-steel vertical-shaft impactor and to double comminution efficiency by combining the conventional stone-on-steel and stone-on-stone vertical-shaft impactors: in both cases with the energy consumption of only one.
U.S. Pat. No. 6,032,889 (Trasher, A) describes and autogenous rotor which is balanced by steel balls in a circular tube attached to the rotor for reducing vibration of the rotor. Such balance system has been known for over a hundred years, such as U.S. Pat. No. 229,787 (Withee). Recent publications on this system can be found in Julia Marshall: Smooth grinding (Evolution, business and technology magazine from SKF, No. 2/1994, pp. 6-7) and in Auto-Balancing by SKF (publication 4597 E, 1997-03).
The known devices for loading and simultaneously accelerating granular materials by co-rotating impact and then making them collide for secondary impact, with the aim of breaking or comminuting, has been found to have certain drawbacks.
For example, because of fully deterministic behaviour, in the known synchrocrusher primary impact takes place at the co-rotating impact plates at concentrated areas which causes high wear rates at these points. Compared with a conventional single impact crushers, where stationary impact takes place against an armoured ring and wear is spread over a great number (10 to 20) of stationary impact plates, co-rotating impact in the known synchrocrusher is concentrated at the centre of a limited number (3 or 4) of co-rotating impact plates, which consequently wear-off much faster than an armoured ring. On the other hand, co-rotating impact avoids impact disturbance along corners and edges of the impact plates, which increases impact intensity dramatically and limits total wear. Although in the known synchrocrusher total impact wear to achieve a specific comminution intensity is normally significantly lower; when compared with a conventional single impact crusher, co-rotating impact plates have normally to be exchanged more frequently than stationary impact plates. However, the limited number of impact plates make it possible to use extremely hard (and expensive) wear resistant material with a very long stand time; for example tungsten carbide which has proven to be most suitable for this purpose. Still, standtime can be relatively short.
Another problem with the known synchrocrusher is the construction of the rotor in which the co-rotating impact members have to be aligned strongly eccentrically, when seen from the radial line between the axis of rotation and the co-rotating impact member, which causes an irregular and complicated stress pattern in the rotor. This makes it necessary to design the rotor construction relatively heavy, which consumes additional rotational energy and requires stronger shaft and bearings; amongst others. Also the suspension of the co-rotating impact members is rather complicated, making it difficult to exchange wear parts.
Furthermore, the known synchrocrusher does not allow for co-rotating impact to take place against a co-rotating autogenous bed of own material, which would limit wear significantly but has a lower level of comminution intensity; however the comminution efficiency of such autogenous impact is high.
The object of the invention is therefore to provide a device which does not exhibit these drawbacks, or at least does so to a lesser extent. This object is achieved by means of making a material collide in a synchrocrusher in which the rotor is designed with a symmetric configuration; that is, the rotor contains equal numbers of respectively forward and backward directed guide members and co-rotating impact members which are or can be arranged, as associated (synchronized) pairs, in each direction of rotation; which pairs are circumferentially disposed uniformly at equal angular distances around the axis of rotation with the forward and backward directed configurations mirror imaged (symmetrically) to each other. By combining or joining together pairs of respective forward and backward directed guide and co-rotating impact members, in respective guide and impact combinations and guide and impact units, supersymmetry is achieved. Such supersymmetry is very effective and allows for many interesting supersymmetrical configurations.
Most important of all, a symmetrical configuration allows for the rotor to operate in both forward and backward direction of rotation, effectively doubling the standtime of the rotor. A supersymmetrical configuration makes it possible to increase the number of forward and backward co-rotating impact members and associated guide members dramatically, increasing standtime with four times and more when compared with the known synchrocrusher. As will be explained later symmetrical guide combinations allow for a design which does not essentially hinder the particle flow to proceed from the meter face to the respective central feeds of the guide members; and therefore does allow for maximum capacity. Very interestingly, the guide and impact combinations and units can be designed in such a way that they take their respective forward and backward position automatically under influence of the rotational force applied only, as will be explained later.
Furthermore, a supersymmetric design allows for the guide and impact combinations and units to create essentially only circumferentially regularly distributed radially directed forces resulting in a regularly distributed stress pattern in the rotor construction, which makes it possible to construct the rotor relatively light and simple; in particular when the combinations and units are pivotly attached to the rotor avoiding bending moments at these locations. Supersymmetrically designed combinations, in particularly units of guiding and impact members, are eminently suitable for such pivotly attachment which makes them also easy to replace; pivotly attachment is therefore a preferred option. Both the combination and units can be designed and attached in different ways as will be explained later.
Moreover, by positioning pairs (units) of co-rotating impact members together, front to front, a symmetrical inward directed acute cavity is formed between the impact faces, in which cavity a bed of own material can accumulate under influence of centrifugal forces, creating autogenous or semi-autogenous impact faces depending on the precise way (distance of each other) the impact faces are positioned. This makes it possible to limit wear to a considerable degree, all the more because after impact the material is guided downwards in front of these cavities and accelerated underinfluence of gravitational force; the material therefore leaves the rotor in a rather xe2x80x9cnatural wayxe2x80x9d avoiding extreme wear along the inner bottom edges (tips) of the rotor, which is a major cause of concern with conventional autogenous rotors, where the particles leave the rotor in horizontal direction (plane of rotation) causing great wear along the tip ends. Autogenous impact has limited comminution efficiency (defined as the amount of new surface produced per unit of externally applied energy for unit mass of material) which level can however be significantly be increased by creating a semi-autogenous impact face where the particles hit partly own material and partly the impact face against which the autogenous bed accumulates. However, comminution efficiency of such autogenous impact is generally very good; for example when the purpose of the comminution process is to clean or shape the particle material.
Furthermore, the device of the invention make it possible to design the rotatable collision means (or co-rotating impact members) as a co-rotating autogenous ring, avoiding impact wear altogether, while wear along the inner bottom edge of such autogenous ring, along which the material leaves the rotor, is limited as explained before. Such a co-rotating autogenous ring can of course also be operated in one direction of rotation only. The possibility to reverse the direction of rotation has however the advantage that it is possible to clean up (freshen) the bed of own material; that is, such autogenous ring has a strong tendency to accumulate a huge (predominantly) amount of fines, creating a so called dead bed which reduces the autogenous intensity.
Finally, the device of the invention make it also possible to apply a configuration that is indirect symmetrical; that is assembling one directional impact members in a co-rotating autogenous ring, which impact members are each associated with either a forward or a backward directed guide member. Such indirect symmetrical configuration makes it possible to operate the rotor as a steel impact crusher in one direction of rotation and as an autogenous impact crusher in the opposite direction of rotation.
To reduce vibration which occurs when the rotor becomes unbalanced, for example because of non-regular wear development of the different wear parts, a circular hollow balance ring can be placed on the rotor, which balance ring is at least partly filled with oil and contains one or more balls which are composed of a steel alloy, chrome steel of tungsten carbide, or a ceramic material. The rotor can be equipped with one balance ring which can contain coarser balls or two or more balance rings which fit into each other and can contain smaller balls. The balance rings can also be placed on top of each other or at different levels.
During co-rotating impact the particles are simultaneously loaded and accelerated for direct secondary impact, as is the case in he known synchrocrusher. Here secondary impact can be applied more effectively then is the case with the known synchrocrusher, because secondary impact members can also be equipped with both forward and backward directed impact faces doubling their standtime.
So, the device of the invention for making material collide in an essentially deterministically, synchronously and (super)symmetrically manner offers a considerable number of interesting possibilities for practical applications.
The discussed objectives, characteristics and advantages of the invention, as well as others, are explained, in order to provide better understanding, in the following detailed description of the invention in conjunction with the accompanying diagrammatic drawings.